This invention relates to an excavator for excavating ground to construct an underground continuous wall and a construction method using the excavator in civil engineering and construction works.
In constructing such an underground continuous wall according to a prior art technique, first a hole of an elliptical section having a 2 to 3 m major axis is dug in the ground to a predetermined depth by a powerful bucket or a hole is dug to a predetermined depth by two or three series of auger drills. After the hole is formed slurry is sealed with a bentonite solution to prevent further penetration of slurry, a reinforcing bar cage is placed in the hole and a ready mixed-concrete is then poured into the hole to form a foundation column. Such a method is repeated to form an underground continuous wall.
With the underground continuous wall constructing method of the prior art described above, the processes are complicated and hence take much time for the completion of the continuous wall. Moreover, slurry or bentonite solution layers at joints between successive columns interrupts the formation of the continuous wall so that after completion of the wall, ground water tends to leak into the inside of the continuous wall through the joints. It is therefore very difficult to provide an underground continuous wall simultaneously having two functions, to serve as a foundations wall and a diaphragm wall.
Moreover, in order to improve the ground in connection with construction of the underground continuous wall in the past, there had been a ground improving method wherein the ground is excavated with earth augers or the like, and at the same time a stabilizer is forcedly mixed with the earth and sand by agitator blades or the like. However, the operations of the method cannot be continuously carried out but only intermittently performed and hence with inefficiency.
Furthermore, in constructing underground wall piles (referred to sometimes as "elliptical piles") having substantially rectangular cross-sections as seen in a plan view, in the past, rectangular holes were formed by excavating the ground by clam buckets or manually. However, such operations are inefficient and dangerous.
Moreover, in removing underground obstacles such as rocks, concrete blocks and the like in the past, rock augers or the like were used to crush them and thereafter they were removed. Such operations are inefficient because of involving extra processes using an additional apparatus other than that used in the construction method of the underground continuous wall.